The present invention relates to plastics articles, especially plastics articles forming elements of moving sealing devices, particularly for machines for producing and/or dispensing food products, such as the pistons of piston-type delivery cocks used in “soft”-type ice cream making machines, or the doors that close the ice cream delivery mouths of batchwise ice cream making machines, or more generally any moving closing element that requires a leaktight seal.
These elements have hitherto been fitted with O-rings seated in semicircular-section grooves formed in the actual article. However, in machines for producing and/or dispensing food products this sealing system has serious drawbacks in terms of hygiene because quantities of product get into the interstices between the grooves housing the O-rings and the O-rings themselves, from where the product is difficult to remove using the automatic washing cycles of these machines, and, given that such products are usually highly perishable, such as for example ice cream, its presence is a not insignificant source of bacterial contamination.
Furthermore, efficient cleaning of such elements would require removing the said O-rings from their seats, which would waste a lot of time and could damage the O-rings, possibly irreparably.
The object of the present invention is therefore to provide a method for the production of sealing elements on plastics articles, that will eliminate the disadvantages of the O-rings used at present and that will be easy and inexpensive to put into practice.
In accordance with the main characteristic of the present invention, this method consists in the production of a film of a silicone material on the sealing surface of the article. Advantageously, this film is co-moulded or co-extruded with the plastics article itself. The thickness of this film may vary from a few tenths of a millimetre to a few millimetres. In particular, in the case of cylindrical elements, such as the pistons of the delivery cocks of ice cream machines, this film preferably covers the whole cylindrical side wall of the piston, while in the case of flat elements this film covers only the sealing surface of this element. In both cases, the film covers the entire active surface of the element which seals, i.e., the surface of the element which abuts an adjacent surface in the food processing machine.
The advantages presented by the present method will be obvious. The silicone surfaces covering the articles have no roughnesses or nooks and crannies and can be washed completely clean with the greatest ease and simplicity. What is more, the cost of manufacture of these articles is much less than that of conventional articles fitted with O-rings.